Design

Setting

Participants

5887 adults aged 35–60 years, who smoked and had evidence of early chronic obstructive pulmonary disease (ie, had an FEV1/FVC [forced expiratory volume at 1 sec/forced vital capacity] interval of ≤70%, and an FEV1 of 55–90% of predicted normal).

Assessment of risk factors

Smoking status was assessed at baseline and at 5 annual visits thereafter. Participant reports of abstinence were confirmed by salivary cotinine concentrations (<20 ng/ml) or if nicotine substitution therapy was used, by CO concentrations (<10 ppm in end tidal expired air). Participants were classified as sustained quitters (verified non-smokers at the first follow up visit, who remained abstinent at all subsequent follow up visits, and who recalled no month with average smoking >1 cigarette/d, starting 4 mo after study entry); continuous smokers (reported smoking at all 5 annual visits), and intermittent smokers (verified non-smokers at ≥1 annual visit and reported smoking at ≥1 annual visit).

Main outcome measures

FEV1 assessed using spirometry (after bronchodilator use) and change in FEV1 reported as a percent of predicted normal, adjusted for African-American and Asian participants.

Main results

149 participants who died, 66 participants who reported lung cancer during follow up, and 21 participants with extreme FEV1 values were excluded from the analysis. At 5 years, sustained quitters had the highest FEV1 (79.8), followed by intermittent quitters (77.9), and continuous smokers (73.1). From years 1 to 5, sustained quitters had the smallest annual rate of loss in FEV1 predicted (loss of 0.33%/y), followed by intermittent quitters (loss of 0.58%/y), and continuous smokers (loss of 1.18%/y). Continuous smokers lost the most lung function at all doses of cigarettes; intermittent smokers who had 1 change in smoking status did better than continuous smokers, and those who had ≥2 changes did even better. Multivariate analysis found that men who were sustained and intermittent quitters had better FEV1% predicted but no difference in FEV1 change when compared with continuous smokers. Women had the same pattern for FEV1% predicted but intermittent smokers had a lower FEV1 than continuous smokers.

Conclusion

Adults who attempted to stop smoking (and may have relapsed) lost less pulmonary function, and lost function less rapidly, than people who smoked continuously, given the same average dose of cigarettes over a 5 year period.

Commentary

Despite broad consensus that stopping smoking reduces the decline in lung function caused by smoking, little has been published on the effects of relapsed smoking cessation. One study found that participants who attempted to stop smoking and then relapsed had steeper rates of decline in FEV1 compared with participants who continued to smoke without attempting to stop,1 which contradicts the findings of this study by Murray et al.

The authors used data from a randomised controlled trial of a smoking cessation intervention to examine the association between multiple smoking cessation attempts with relapses to smoking and pulmonary function in adults. The study design was robust—inclusion and exclusion criteria were explicit, as were those for the construction of the study categories (ie, quitters, continuous smokers, and intermittent smokers). The authors accounted for sex differences, ethnicity, number of cigarettes smoked, and for potential errors in lung function measurement by using spirometry. They excluded patients who died during the study or were diagnosed with lung cancer. Smoking cessation was verified using either salivary cotinine levels or CO concentrations, thus eliminating the potential for participant misreporting of smoking.

The results of the study can be used by nurses in the context of providing individual advice and public health education on the benefits of smoking cessation. Smokers who attempted to stop smoking but relapsed lost less pulmonary function and lost pulmonary function less rapidly than people who did not attempt to stop: in other words, trying to stop smoking was beneficial, even if it was not maintained. Also, Murray et al suggest that women seemed to benefit more from stopping smoking than men because, for some reason, women's lung function deteriorates more rapidly than men's with continued smoking.

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Copyright 1999 by the RCN Publishing Company and BMJ Publishing Group for Evidence-Based Nursing